Can I be experiencing muscle atrophy from being bed ridden for 3 weeks?

Possible. It is amazing how quickly lack of activity can impact the body. Muscle weakness, and even loss of muscle mass is a common and quick effect of illness and being bedridden. I warn patients that for every day in bed especially if critically ill, it can take 4 days of therapy to regain strength to the previous level. Activity is so important for overall and muscle health!